1. Field of Invention
The present invention relates to a picture image input method which optically inputs the picture image of an original medium.
2. Description of Related Art
A picture image input apparatus (scanner) optically inputs and photoelectrically converts the picture image of an original medium, and outputs this picture image as electronic data.
In this kind of scanner, when the picture image of an original medium is input, a look-up table (LUT) is necessary in order to reproduce the object image. This look-up table is, for example, one in which a table used to revise variances characteristic of the apparatus and a table used for picture image adjustment according to commands from the user are merged.
In the picture image input of a negative film (negative original medium) which is a transmissive original medium, the negative gradation conversion table which is used to convert the negative to a positive is also merged into the look-up table.
Furthermore, in the picture image input of a negative film, it is necessary to perform a prescan in order to create this negative gradation conversion table. With the exception of creating the negative gradation conversion table, this prescan performs the same actions as the normal scan during picture image input.
This negative gradation conversion table creation is started, for example, by commands from a host computer to which the scanner is connected.
First, the scanner receives from the host computer the resolution, the picture image input range and the data in the look-up table into which the negative gradation conversion table which is the basis is merged. Furthermore, the scanner, upon receiving from the host computer a command to start scanning, starts the prescan using this look-up table.
Next, the scanner creates a histogram of the brightness of the input picture image and the frequency thereof from the picture image data input through the prescan.
Furthermore, a shadow point used to match a white point is found from this histogram. The white point is the location where the value of the output of the negative gradation conversion table is a maximum. In addition, the shadow point is the darkest location on the negative film, and is the brightest location in the original object. That is to say, the white point is the brightest location in the original object, and is the point which should be the brightest location in the data from the negative-to-positive conversion of the picture image which was input.
For example, from the histogram which is obtained, the brightness value is added in the high direction from level 0, and the value immediately prior to where the cumulative frequency value crosses 0.3% (cumulative frequency coefficient 1) of the total is made the shadow point S.
Conversely, the frequency value is added from the maximum level (4095 in the case of a 12-bit table) in the low direction, and the value immediately prior to where the cumulative frequency value crosses 0.03% (cumulative frequency coefficient 2) of the total is made the highlight point H.
Through the above, the highlight point and shadow point of the negative gradation conversion table are determined.
In the scanner, the negative gradation conversion table obtained as described above is merged into the look-up table, and the picture image data input by the actual picture image input is converted using this and is sent to the host computer.
However, in the above-described prescan the following problems arise because the resolution is fixed regardless of the region over which the picture image is input.
First, when the region in which the picture image is input in the prescan is widened, the data volume which is input increases, causing the time needed for the prescan action to become long.
On the other hand, when the region in which the picture image is input in the prescan is made too small, the data volume which is input diminishes, so that accuracy in the obtained histogram cannot be achieved, and as a result, the quality of the negative gradation conversion table that is obtained worsens